Back and neck pain are the leading causes of disability and lost productivity for American workers under the age of 45. Degenerative disc disease and its sequelae, whereby the fibrocartilaginous disc between adjacent vertebral bodies loses height, hydration and structural integrity, is one of the most common causes of back and neck pain and may develop secondary to traumatic injuries, inflammatory processes or various degenerative disorders. When conservative treatment fails, surgical fusion of the vertebral segments across the abnormal disc may be the only currently available procedure for pain relief. An increasing number of these spinal fusions are performed each year. It is estimated that over half a million of these procedures were performed in the United States last year alone.
Various surgical approaches to abnormal lumbar disc spaces are employed and include anterior interbody fusions, posterior interbody fusions and tranforaminal fusions. At cervical levels, an anterior approach is often employed. These procedures may be augmented by various posterior element instrumentation techniques. Regardless of the surgical approach, the goal is to achieve solid bony fusion between the involved endplates and eliminate the symptoms caused by motion and associated degenerative and other reactive changes between these unstable vertebral segments.
The first lumbar fusion procedures involved removal of a portion of the abnormal disc and placement of autologous bone graft material in the disc space without other instrumentation in the vertebral bodies or posterior elements. This approach often failed due to inadequate structural integrity. Subsequently, cortical bone dowels and femoral ring allografts were employed in an attempt to restore disc space height and augment structural integrity. After U.S. Pat. No. 4,961,740 (“Ray, et al.”) introduced the concept of the threaded cylindrical interbody fusion cage in 1990, numerous other interbody fusion devices were developed. These devices include cylindrical, rectangular, and tapered cages and spacers composed of metals, polymers, human bone allograft and other materials. Some of these devices incorporate or are coated with human bone morphogenetic protein or other agents to promote new bone formation and accelerate fusion. Despite these advancements, failure rates for spinal fusion surgeries remain unacceptably high, greater than 10 percent in most series.
Therefore, there is a need in the art for an improved method to effect a more rapid, reliable fusion between unstable vertebral segments and avoid the considerable medical and economic impact of failed spinal fusions.